This proposal describes projects from four neighboring laboratories, united by their common interest in a deeper understanding of the replication of animal viruses. The four groups will use a combination of genetic and biochemical techniques to obtain detailed molecular information about various steps of the viral life cycle and will share reagents, technology and expertise throughout the work. The collaborative projects span all phases of viral growth, from the initiation and regulation of transcription of viral mRNAs immediately after infection, through the replication of the viral genome, to the final assembly of progeny virion particles. These analyses of viral gene expression and function are important in furthering our understanding of each specific virus under study, and furthermore should help reveal principles of general significance for the replication of all viruses and indeed for the activities of mammalian cellular genes as well. The viruses targetted for study, and the steps of the life cycle to be analyzed are: In the herpes simplex virus system, the aim is to unravel the complex interplay of transcriptional regulatory factors that determine the timing of gene activation and inactivation during the course of infection. In the adenovirus system, we will make use of viral constructs carrying duplicated promotors to analyze in detail the phenotype and biochemical consequences of mutations placed in the major later promoter and the divergent transcription unit that emanates from it. In the poliovirus system, we will analyze the genomic sequences necessary for template recognition by the viral RNA polymerase, and identify functional regions of the polymerase by site-directed mutagenesis. Finally in the murine retroviruses, the goal is to determine those regions and subregions of the viral gene products required for the assembly of virions and for the correct incorporation of proteins into progeny virus particles. The results of each of these studies should provide important new information concerning the replication of each of the representative members in this collection of diverse viral classes.